JP5843682B2 - Diffusion layer structure of fuel cell - Google Patents

Description

  The present invention relates to a diffusion layer structure of a fuel cell. More specifically, the present invention relates to a diffusion layer structure of a polymer electrolyte fuel cell.

  2. Description of the Related Art In recent years, fuel cells that generate electricity by electrochemical reaction of reaction gases have attracted attention as new power sources for automobiles. A fuel cell is preferred in terms of high power generation efficiency because it directly obtains electricity through an electrochemical reaction. Further, since the fuel cell generates only harmless water during power generation, it is considered preferable from the viewpoint of environmental impact.

  For example, a polymer electrolyte fuel cell has a stack structure in which several tens to several hundreds of cells are stacked. Each cell is configured by sandwiching a membrane electrode structure (MEA) between a pair of conductive separators. The membrane electrode structure is composed of an anode electrode (cathode) and a cathode electrode (anode), and an electrolyte membrane made of a sulfonic acid resin sandwiched between these electrodes. Both electrodes include an electrode catalyst layer containing a platinum-based metal catalyst in contact with the electrolyte membrane, and a conductive diffusion layer in contact with the electrode catalyst layer and for supplying a reaction gas and discharging generated water. The separator has a fuel gas channel formed on one surface thereof and an oxidant gas channel formed on the other surface thereof.

  In the polymer electrolyte fuel cell having the above-described configuration, hydrogen as fuel gas is supplied to the anode electrode via the fuel gas flow path. In addition, air as an oxidant gas is supplied to the cathode electrode via the oxidant gas flow path. Then, hydrogen supplied to the anode electrode is protonated on the electrode catalyst layer, and the generated proton moves to the cathode electrode through the electrolyte membrane. At this time, electrons generated together with protons are taken out to an external circuit and used as electric energy.

  By the way, since the conductivity of the electrolyte membrane is significantly reduced when moisture is lost, the fuel gas and the oxidant gas are usually humidified in advance and supplied into the cell. In that case, it is important to supply fuel gas and oxidant gas efficiently by the diffusion layer and to smoothly discharge generated water. For this reason, various studies have been conducted on the pore diameter and density (porosity) of the diffusion layer, water repellency, and the like.

  For example, a fuel cell diffusion layer is disclosed in which a conductive water-repellent layer is provided on a gas diffusion substrate and the pore diameter of the conductive water-repellent layer is defined within a predetermined range (see Patent Document 1). Further, a porous carbon sheet is disclosed as a diffusion layer formed by binding carbon fibers with resin carbide and defining the pore diameter and the carbon fiber diameter within a predetermined range (see Patent Document 2).

JP 2010-129310 A International Publication No. 2007/037084

  By the way, the conventional fuel cell exhibits stable power generation performance by controlling the flow rate of the humidified gas and the load current value within a certain range when the operation state is a steady state. However, in automotive applications where the driving state changes every moment, the current situation is that stable power generation performance is not obtained, and there is a demand for a fuel cell capable of obtaining high power generation performance regardless of the driving state. In particular, in consideration of starting from normal temperature, a fuel cell that can stably obtain high power generation performance regardless of the humidified state in a wide temperature range from normal temperature to 80 ° C. or more is required.

  The present invention has been made in view of the above, and an object of the present invention is to provide a diffusion layer structure of a fuel cell that can stably obtain high power generation performance in a wide temperature range regardless of the humidified state.

［式（１）中、厚みは上記拡散層の厚み（μｍ）を表し、空孔率は上記拡散層の空孔率（％）を表し、平均流量細孔径は上記拡散層の平均流量細孔径（μｍ）を表す。］ In order to achieve the above object, the present invention is disposed in a membrane electrode structure (for example, a membrane electrode structure 20 described later) in which electrodes are provided on both sides of an electrolyte membrane (for example, a polymer electrolyte membrane 21 described later). A diffusion layer structure (for example, a later-described diffusion layer structure 10) of a fuel cell (for example, a polymer electrolyte fuel cell 1), the diffusion layer (for example, a later-described diffusion layer 11), and the above-described electrolyte membrane side A microporous layer (for example, microporous layer 12 described later) formed mainly on carbon and a fluororesin, and having a flow rate of 2 L / min with respect to the diffusion layer having a transmission area of 1.86 cm ² . When the actual measurement value of the pressure loss generated when the air permeates is P1, and the theoretical value of the pressure loss defined by the following formula (1) is P2, the ratio P1 / P2 of the P1 to the P2 is: 2 to 15 and the microporous layer The fuel cell diffusion layer structure is characterized by having a hydraulic pressure of 5 to 180 kPa.

[In the formula (1), the thickness represents the thickness (μm) of the diffusion layer, the porosity represents the porosity (%) of the diffusion layer, and the average flow pore diameter represents the average flow pore diameter of the diffusion layer. (Μm). ]

In the present invention, a microporous layer mainly composed of carbon and fluororesin is provided on the diffusion layer on the electrolyte membrane side. Further, the ratio P1 / P2 of the actually measured value P1 to the theoretical value P2 of the pressure loss of the diffusion layer represented by the above formula (1) is set within the range of 2-15.
Here, the ratio P1 / P2 of the actual measurement value P1 to the theoretical value P2 of the pressure loss of the diffusion layer is a parameter correlated with the flexibility of the pores in the diffusion layer. That is, the larger the value of P1 / P2, the higher the flexibility of the pores in the diffusion layer, which means that the pores are winding. Therefore, by limiting the value of P1 / P2 within the range of 2 to 15, the flexibility of the pores can be suppressed, so that the pressure loss of the diffusion layer is suppressed, and the water vapor generated at the electrode is efficiently discharged. . Therefore, the oxygen partial pressure in the vicinity of the electrode can be increased, and the power generation performance can be improved. In addition, since the water vapor is efficiently discharged, the condensation of the water vapor at a low temperature is suppressed, and the occurrence of flatting can be suppressed. Therefore, according to the present invention, high power generation performance can be obtained in a wide temperature range from a low temperature range to a high temperature range. In particular, high power generation performance can be obtained at low temperature and high humidity.

  Moreover, in this invention, while setting said P1 / P2 in the said range, the water-permeable pressure of a microporous layer is set in the range of 5-180 kPa. Thereby, it is possible to suppress the generated water generated at the electrode from being discharged through the microporous layer, and the generated water can be held on the electrode side. Therefore, the membrane electrode structure can be moisturized and high power generation performance can be obtained regardless of the humidified state. In particular, high power generation performance can be obtained at high temperature and low humidity.

  ADVANTAGE OF THE INVENTION According to this invention, the diffusion layer structure of the fuel cell which can obtain stably high electric power generation performance in a wide temperature range irrespective of a humidification state can be provided.

It is a figure which shows typically the diffusion layer structure of the polymer electrolyte fuel cell which concerns on one Embodiment of this invention. It is a figure which shows the structure of a pressure loss measuring apparatus, (A) is a figure which shows the whole structure, (B) is a top view of the ventilation ring of a pressure loss measuring apparatus. It is a figure which shows the relationship between the pressure measured by the bubble point method using a palm porometer, and flow volume. It is a figure which shows the relationship between P1 / P2 and a terminal voltage. It is a figure which shows the relationship between the hydraulic pressure of a microporous layer, and a terminal voltage.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
FIG. 1 is a diagram schematically showing a diffusion layer structure 10 of a polymer electrolyte fuel cell 1 according to an embodiment of the present invention. FIG. 1 shows the configuration of the cathode side of the polymer electrolyte fuel cell 1, and the diffusion layer structure 10 according to this embodiment is applied only to the diffusion layer on the cathode side of the polymer electrolyte fuel cell 1. Yes.

  The polymer electrolyte fuel cell 1 has a stack structure in which dozens to hundreds of cells (not shown) are stacked. Each cell is configured by sandwiching a membrane electrode structure (MEA) 20 between a pair of conductive separators. As shown in FIG. 1, an oxidant gas flow path 31 is formed in the separator 30 on the cathode side.

The membrane electrode structure 20 includes a solid polymer electrolyte membrane 21, and a cathode electrode catalyst layer 22 and an anode electrode catalyst layer disposed on both sides of the solid polymer electrolyte membrane 21.
The solid polymer electrolyte membrane 21 is formed, for example, by impregnating water with a thin film of perfluorosulfonic acid. The cathode electrode catalyst layer 22 and the anode electrode catalyst layer include porous carbon particles having platinum or the like supported on the surface. The diffusion layer structure 10 according to this embodiment is disposed on the cathode side of the membrane electrode structure 20.

  The diffusion layer structure 10 according to this embodiment includes a diffusion layer 11 and a microporous layer 12. The diffusion layer 11 is disposed in contact with the separator 30. The microporous layer 12 is formed on the diffusion layer 11 and is disposed in contact with the cathode electrode catalyst layer 22.

  The diffusion layer 11 has a function of diffusing oxygen as an oxidant gas and efficiently supplying oxygen to the entire cathode electrode catalyst layer. As the diffusion layer 11, carbon paper containing carbon fiber and carbonized resin (binder resin) is water-repellent treated with a fluororesin such as tetrafluoroethylene-hexafluoropropylene (FEP) or polytetrafluoroethylene (PTFE). Used.

  By the way, when the diffusion layer is arranged in direct contact with the cathode electrode catalyst layer, the generated water generated in the cathode electrode catalyst layer penetrates into the diffusion layer, and a flooding phenomenon occurs. When the flatting phenomenon occurs, the supply of oxygen to the solid polymer electrolyte membrane is hindered, and the power generation performance decreases. Further, once the generated water is accumulated in the diffusion layer, it is not easy to remove the accumulated generated water.

  Therefore, in the present embodiment, the microporous layer 12 is disposed between the cathode electrode catalyst layer 22 and the diffusion layer 11. As shown in FIG. 1, the microporous layer 12 has a characteristic of allowing water vapor and oxygen to permeate but not liquid water. By arranging the microporous layer 12 having such characteristics between the cathode electrode catalyst layer 22 and the diffusion layer 11, the occurrence of the flooding phenomenon in the diffusion layer 11 is suppressed.

  The microporous layer 12 is mainly composed of carbon and a fluororesin. As the carbon, for example, an air-layered carbon fiber is used. As the fluororesin, for example, tetrafluoroethylene-hexafluoropropylene (FEP) is used.

  The microporous layer 12 is formed by preparing a paste containing carbon and a fluororesin, applying the paste on the diffusion layer 11 and heat-treating the paste. Or you may use what was formed in the sheet form separately from the diffusion layer 11 using the said paste.

In the present embodiment, when the actual measurement value of the pressure loss generated when air passes through the diffusion layer 11 is P1, and the theoretical value of the pressure loss of the diffusion layer 11 defined by the above formula (1) is P2, The ratio P1 / P2 of P1 to P2 is set in the range of 2-15. If the value of P1 / P2 is within this range, high power generation performance can be obtained stably over a wide temperature range regardless of the humidified state.
In addition, as a method of adjusting the value of P1 / P2 within the range of 2 to 15, for example, there is a method of changing the content ratio of carbon fiber and carbonized resin (binder resin) in the carbon paper constituting the diffusion layer 11. Can be mentioned.

Here, a method of measuring the actual measurement value P1 of the pressure loss that occurs when air permeates through the diffusion layer 11 will be described in detail.
2A and 2B are diagrams illustrating the configuration of the pressure loss measuring device 50, where FIG. 2A is a diagram illustrating the overall configuration, and FIG. 2B is a plan view of the ventilation ring 510 of the pressure loss measuring device 50.

  As shown in FIG. 2A, the pressure loss measuring device 50 includes a base 51, a holder 52 that holds and holds the measurement sample S (diffusion layer 11), and a mass flow that controls the flow rate and supplies air. A controller 53, a load cell 54 for applying a load in the thickness direction to the measurement sample S, an air introduction part 56 into which air is introduced, and an air discharge opened to the atmosphere to discharge air that has passed through the measurement sample S And a differential pressure gauge 55 that measures the differential pressure between the air introduction part 56 and the air discharge part 57.

As shown in FIG. 2, the holder portion 52 is provided on the upper plate portion 521 and the lower plate portion 522 that are substantially horizontal and opposed to each other, and the upper plate portion 521 and the lower plate portion 522, respectively. Ventilation rings 510 and 510 provided at positions facing each other.
As shown in FIG. 2B, the ventilation ring 510 has a cylindrical shape, and an annular groove 512 is formed in the inside thereof. The groove portion 512 is formed to open to the measurement sample S side. In addition, two holes 511 and 511 that open to the air introduction part 56 or the air discharge part 57 are provided on the connection surfaces 513 and 513 with the upper plate part 521 or the lower plate part 522 of the ventilation rings 510 and 510, respectively. It has been. Thereby, air is introduced from the air introduction part 56 into the groove part 512 of the ventilation ring 510 provided in the lower plate part 522 through the hole parts 511 and 511. Further, the air that has passed through the measurement sample S is introduced into the groove 512 of the ventilation ring 510 provided in the upper plate portion 521, and is discharged to the air discharge portion 57 through the holes 511 and 511.

The procedure for measuring the pressure loss of the diffusion layer 11 by the pressure loss measuring device 50 is as follows.
First, the measurement sample S (diffusion layer 11) is set on the holder portion 52 via the ventilation rings 510 and 510. Next, a predetermined load is applied to the measurement sample S downward by the load cell 54. Next, supply of air from the mass flow controller 53 is started. Then, air is introduced from the air introduction part 56 into the groove part 512 of the ventilation ring 510 provided in the lower plate part 522 through the hole parts 511 and 511. The air supplied to the groove portion 512 of the ventilation ring 510 passes through the measurement sample S and is introduced into the groove portion 512 of the ventilation ring 510 disposed to face the upper plate portion 521. Then, the air is discharged to the air discharge portion 57 through the holes 511 and 511. At this time, the differential pressure between the air introduction part 56 and the air discharge part 57 is measured by the differential pressure gauge 55. Thereby, the actual measurement value P1 of the pressure loss (transmission pressure loss) of the measurement sample S (diffusion layer 11) is measured.

Note that the measurement conditions of the pressure loss measuring device 50 may be that the transmission area of the measurement sample S (diffusion layer 11) is 1.86 cm ² and the flow rate of supplied air is ² L / min. Further, the gas pressure (injection pressure to the air introduction unit 56) may be 100 kPaG, and the measurement surface pressure may be 15 kgf / cm ² .

［式（１）中、厚みは上記拡散層の厚み（μｍ）を表し、空孔率は上記拡散層の空孔率（％）を表し、平均流量細孔径は上記拡散層の平均流量細孔径（μｍ）を表す。］ Next, the theoretical value P2 of the pressure loss of the diffusion layer 11 will be described in detail.
The theoretical value P2 of the pressure loss of the diffusion layer 11 is defined by the following formula (1).

[In the formula (1), the thickness represents the thickness (μm) of the diffusion layer, the porosity represents the porosity (%) of the diffusion layer, and the average flow pore diameter represents the average flow pore diameter of the diffusion layer. (Μm). ]

Here, as an expression expressing the pressure loss (permeation pressure loss) of a single fluid in the fixed packed bed, the Cozeny Kalman expression is known. This equation is obtained by regarding the flow path in the layer as a collection of uniform capillaries and applying the Poiseuille equation. Therefore, if the pressure loss of air in the diffusion layer 11 is ΔP, ΔP is expressed by the following formula (2).

  In the above formula (2), the thickness (μm) of the diffusion layer 11 can be used as the pore length. As the pore diameter, an average flow pore diameter (μm) can be used. Since α is a constant, it can be seen that the theoretical value P2 of the pressure loss of the diffusion layer 11 can be defined as in the above equation (1) based on the above equation (2).

The average flow pore size is measured by a bubble point method using a palm porometer (for example, a palm porometer manufactured by PMI).
Here, the bubble point method is a method for determining the maximum pore diameter and the minimum pore diameter of a sample by measuring the pressure required to push out the liquid filled in the pores by surface tension and capillary action. is there.

FIG. 3 is a diagram showing the relationship between pressure and flow rate measured by the bubble point method using a palm porometer. As shown in FIG. 3, in the bubble point method, a wet flow curve is obtained and a dry curve is obtained by measuring each of a wet state and a dry state of the sample. At this time, the point at which the flow rate starts to be detected in the wetting curve represents the maximum pore diameter (bubble point), and the intersection of the wetting curve and the drying curve represents the minimum pore diameter. Then, a 1/2 dry flow curve (half dry curve) in which the flow rate of the dry curve is halved is obtained, and the intersection of the obtained 1/2 dry flow curve and the wet flow curve represents the average flow pore diameter. Yes.
Therefore, in this embodiment, the theoretical value P2 of the pressure loss of the diffusion layer 11 is calculated according to the above formula (1) using the average flow pore diameter measured by the palm porometer.

Moreover, in this embodiment, the hydraulic pressure of the microporous layer 12 is set in the range of 5 to 180 kPa. Here, the hydraulic pressure means a pressure at which water starts to enter. In the present embodiment, the hydraulic pressure of the microporous layer 12 is measured as follows.
First, a microporous layer is formed on carbon paper, and this is used as a measurement sample. Next, 2 ml of pure water is dropped on the microporous layer of the measurement sample to form a water film. As a measuring device, a palm porometer (for example, a palm porometer manufactured by PMI) is used to gradually add air pressure to the water film, which is necessary for pure water to permeate the pores of the measurement sample. Measure the minimum pressure. Let the measured minimum pressure be the water permeation pressure of a microporous layer.
In addition, as a method of adjusting the water permeation pressure of the microporous layer 12 within a range of 5 to 180 kPa, for example, a method of changing the carbon content in the microporous layer 12 may be mentioned.

According to this embodiment, the following effects are produced.
In the present embodiment, the microporous layer 12 mainly composed of carbon and fluororesin is provided on the diffusion layer 11 on the solid polymer electrolyte membrane 21 side. Further, the ratio P1 / P2 of the actual measurement value P1 to the theoretical value P2 of the pressure loss of the diffusion layer 11 represented by the above formula (1) was set within the range of 2-15. Here, the ratio P1 / P2 of the actual measurement value P1 to the theoretical value P2 of the pressure loss of the diffusion layer 11 is a parameter correlated with the flexibility of the pores in the diffusion layer 11. That is, the larger the value of P1 / P2, the higher the flexibility of the pores in the diffusion layer 11, which means that the pores are winding. Therefore, by limiting the value of P1 / P2 within the range of 2 to 15, the flexibility of the pores can be suppressed, so that the pressure loss of the diffusion layer 11 is suppressed, and the water vapor generated in the cathode electrode catalyst layer 22 is reduced. Efficiently discharged. Therefore, the oxygen partial pressure in the vicinity of the cathode electrode catalyst layer 22 can be increased, and the power generation performance can be improved. In addition, since the water vapor is efficiently discharged, the condensation of the water vapor at a low temperature is suppressed, and the occurrence of the flatting phenomenon can be suppressed. Therefore, according to the present embodiment, high power generation performance can be obtained in a wide temperature range from a low temperature range to a high temperature range. In particular, high power generation performance can be obtained at low temperature and high humidity.

  Moreover, in this embodiment, while setting said P1 / P2 in the said range, the water permeation pressure of the microporous layer 12 was set in the range of 5-180 kPa. As a result, the generated water generated in the cathode electrode catalyst layer 22 can be suppressed from being discharged through the microporous layer 12, and the generated water is held on the cathode electrode catalyst layer 22 side to keep the membrane electrode structure 20 moisturized. Therefore, high power generation performance can be obtained regardless of the humidified state, and particularly high power generation performance can be obtained at high temperature and low humidification.

It should be noted that the present invention is not limited to the above-described embodiment, and modifications, improvements, etc. within a scope that can achieve the object of the present invention are included in the present invention.
In the above embodiment, the microporous layer 12 is disposed so as to be in direct contact with the cathode electrode catalyst layer 22, but is not limited thereto. Between the microporous layer 12 and the cathode electrode catalyst layer 22, for example, a water retention layer containing an electrolyte, carbon or the like may be provided. By providing such a water retention layer, fluctuations in power generation performance due to changes in humidification conditions can be further suppressed.

  Next, the present invention will be described in more detail based on examples, but the present invention is not limited thereto.

<Example 1>
(1) Preparation of cathode side diffusion layer and anode side diffusion layer The same diffusion layer was prepared as a cathode side diffusion layer and an anode side diffusion layer. Specifically, the average flow pore size 27 [mu] m, bulk density 0.34 g / c ^{m 3,} the thickness 193 nm, a basis weight 66.5 g / ^{m 2} and a porosity 0.80% of carbon paper, DuPont-Mitsui Fluorochemicals After impregnating a tetrafluoroethylene-hexafluoropropylene copolymer FEP dispersion “FEP 120-JRB” (solid content concentration 54%) manufactured by Chemical Co., Ltd., heat treatment was performed at 120 ° C. for 30 minutes. The impregnation was carried out so that the weight percent of FEP after heat treatment was 2.4 weight percent. As a result, a cathode side diffusion layer and an anode side diffusion layer in which water repellent treatment was performed on carbon paper were obtained.
With respect to the obtained cathode-side diffusion layer, an actual measurement value P1 of the pressure loss of the diffusion layer was measured using the pressure loss measuring device 50 described above, and as a result, it was 1.2 kPa. As the measurement conditions for the actual measurement value P1, the permeation area of the diffusion layer is 1.86 cm ² , the flow rate of the supplied air is ² L / min, the gas pressure (input pressure to the air introduction unit 56) is 100 kPaG, and the measurement surface pressure Was 15 kgf / cm ² (the same applies to Examples 2 to 6 and Comparative Examples 1 to 6).
Further, the theoretical value P2 of the pressure loss was obtained according to the above formula (1), and P1 / P2 was calculated and found to be 6.5. The average flow pore size of the carbon paper was measured using a palm porometer manufactured by PMI (the same applies hereinafter).

(2) Preparation of cathode side microporous layer mixed paste 12g of vapor growth carbon "VGCF" manufactured by Showa Denko KK, which has both electron conductivity and pore-forming property, tetrafluoroethylene-hexafluoropropylene manufactured by Mitsui-DuPont Fluorochemical 20 g of copolymer FEP dispersion “FEP 120-JRB” (solid content concentration 54%) and 200 g of ethylene glycol were weighed, mixed, and stirred by a ball mill. Thereby, a cathode side microporous layer mixed paste was prepared.

(3) Preparation of anode side microporous layer mixed paste 12 g of carbon “Vulcan XC72R” manufactured by Cabot Corporation, tetrafluoroethylene-hexafluoropropylene copolymer FEP dispersion “FEP 120-JRB” manufactured by Mitsui DuPont Fluorochemical Co., Ltd. (solid) (Minute concentration 54%) 20 g and ethylene glycol 155 g were weighed, mixed and stirred by a ball mill. Thereby, an anode side microporous layer mixed paste was prepared.

(4) Preparation of cathode-side microporous layer The cathode-side microporous layer mixed paste prepared in (2) above was screen-printed on the cathode-side diffusion layer prepared in (1) above, and then 380 ° C. for 30 minutes. A heat treatment was performed. This produced the cathode side microporous layer. Screen printing was performed such that the weight of the cathode-side microporous layer per unit area of carbon paper was 1.2 mg / cm ² and the pore volume was 0.25 μL / cm ² . The pore diameter of the obtained cathode-side microporous layer was 1.1 μm as measured using a palm porometer manufactured by PMI. Moreover, thickness was 35 micrometers and the water permeation pressure measured according to the above-mentioned measuring method was 6.0 kPa.

(5) Preparation of anode-side microporous layer After the anode-side microporous layer mixed paste prepared in (3) above was screen-printed on the anode-side diffusion layer prepared in (1) above, the temperature was 380 ° C. for 30 minutes. A heat treatment was performed. This produced the anode side microporous layer. Screen printing was performed such that the weight of the anode-side microporous layer per unit area of carbon paper was 1.2 mg / cm ² and the pore volume was 0.09 μL / cm ² .

(6) Preparation of catalyst paste Weighed so that the weight ratio “DE2020CS” / “LSA” of the ion conductive polymer solution “DE2020CS” made by DuPont to the platinum catalyst “LSA” made by BASF becomes 0.1 The catalyst paste was prepared by stirring with a ball mill.

(7) Preparation of electrode catalyst sheet After applying the catalyst paste prepared in (6) above on a PTFE sheet so that the platinum weight is 0.7 mg / cm ² , heat treatment is performed at 120 ° C. for 60 minutes. did. This produced the cathode side electrode catalyst sheet.
Moreover, after apply | coating the catalyst paste prepared by said (6) so that platinum weight might be set to 0.4 mg / cm < ² > on a sheet | seat made from PTFE, the heat processing for 120 degreeC x 60 minutes were implemented. This produced the anode side electrode catalyst sheet.

(8) Transfer to Polymer Electrolyte Membrane One side of the polymer electrolyte membrane “GORE SELECT” (thickness 20 μm) manufactured by Japan Gore-Tex Co., Ltd. by using the decal method for the cathode side electrode catalyst sheet prepared in (7) above. The anode side electrode catalyst sheet prepared in (7) above was transferred to the other surface of the polymer electrolyte membrane by a decal method. As a result, a cathode electrode catalyst layer was formed on one surface of the polymer electrolyte membrane, and an anode electrode catalyst layer was formed on the other surface.
Here, the transfer by the decal method is to transfer the electrode catalyst layer to the surface of the polymer electrolyte membrane by peeling the PTFE sheet after thermocompression bonding the electrode catalyst layer side of the electrode catalyst sheet to the polymer electrolyte membrane. It is a technique.

(9) Production of membrane electrode structure The cathode side diffusion layer in which the cathode side microporous layer was formed in (4) above and the anode side diffusion layer in which the anode side microporous layer was formed in (5) above, A membrane electrode structure was produced by sandwiching and thermocompression bonding the polymer electrolyte membrane to which the electrode catalyst layer was transferred in (8) above. Thermocompression bonding was performed at 120 ° C. and a surface pressure of 30 kgf / cm ² so that the cathode side microporous layer was in contact with the cathode side electrode catalyst layer and the anode side microporous layer was in contact with the anode side electrode catalyst layer.

(10) Evaluation of power generation performance After the membrane electrode structure produced in (9) above is sandwiched between a pair of metal separators, hydrogen as fuel gas is supplied to the anode side, and oxidant gas is supplied to the cathode side. As a result, the power generation performance was evaluated. As the power generation conditions, cell temperature, anode gas inlet relative humidity, cathode gas inlet relative humidity, anode stoichiometry and cathode stoichiometry were as shown in Table 1. The surface pressure of the electrode part of the membrane electrode structure was 15 kgf / cm ^2, and the area of the electrode part of the membrane electrode structure was 54.3 cm ² . The evaluation results are shown in Table 2.

<Example 2>
In the preparation of (1) a cathode side diffusion layer and an anode side diffusion layer of Example 1, the mean flow pore size 21 [mu] m, bulk density 0.34 g / c ^{m 3,} a thickness 195, basis weight 67 g / ^{m 2} and a porosity 0. The same operation as in Example 1 was performed except that 80% carbon paper was used.
With respect to the obtained cathode-side diffusion layer, an actual measurement value P1 of the pressure loss of the diffusion layer was measured using the pressure loss measuring device 50 described above, and as a result, it was 1.2 kPa. Further, the theoretical value P2 of the pressure loss was obtained according to the above formula (1), and P1 / P2 was calculated and found to be 11.2. The evaluation results are shown in Table 2.

<Example 3>
In the preparation of Example 1 (1) cathode side diffusion layer and an anode side diffusion layer, the mean flow pore size 27 [mu] m, bulk density 0.31 g / c ^{m 3,} a thickness 195, basis weight 60.2 g / ^{m 2} and a porosity The same operation as in Example 1 was performed except that 0.82% carbon paper was used.
With respect to the obtained cathode side diffusion layer, the measured value P1 of the pressure loss of the diffusion layer was measured using the pressure loss measuring device 50 described above, and as a result, it was 1.3 kPa. Further, the theoretical value P2 of the pressure loss was obtained according to the above-described formula (1), and P1 / P2 was calculated and found to be 5.2. The evaluation results are shown in Table 2.

<Example 4>
In preparation of (2) cathode side microporous layer mixed paste of Example 1, 12 g of vapor growth carbon “VGCF” manufactured by Showa Denko KK, tetrafluoroethylene-hexafluoropropylene copolymer FEP manufactured by Mitsui DuPont Fluorochemical Co., Ltd. The same operation as in Example 1 was performed, except that 10 g of the dispersion “FEP 120-JRB” (solid content concentration 54%) and 200 g of ethylene glycol were weighed and mixed. The pore diameter of the obtained cathode-side microporous layer was 0.9 μm as measured using a palm porometer manufactured by PMI. Moreover, thickness was 35 micrometers and the water permeation pressure (henceforth the same) measured according to the above-mentioned measuring method was 14.8 kPa. The evaluation results are shown in Table 2.

<Example 5>
Instead of the cathode-side microporous layer produced in (4) of Example 1, a conductive porous sheet (pore diameter 0.6 μm, thickness 38 μm, hydraulic pressure 45.1 kPa) containing resin and carbon was used. In the production of the membrane electrode structure according to 1 (9), except that the conductive porous sheet was placed on carbon paper so as not to be wrinkled, and bonded to the electrode at 120 ° C. and a surface pressure of 30 kgf / cm ² , The same operation as in Example 1 was performed. The evaluation results are shown in Table 2.

<Example 6>
Instead of the cathode-side microporous layer produced in (4) of Example 1, a conductive porous sheet (pore diameter 0.4 μm, thickness 41 μm, hydraulic pressure 134.4 kPa) containing resin and carbon was used. In the production of the membrane electrode structure according to 1 (9), except that the conductive porous sheet was placed on carbon paper so as not to be wrinkled, and bonded to the electrode at 120 ° C. and a surface pressure of 30 kgf / cm ² , The same operation as in Example 1 was performed. The evaluation results are shown in Table 2.

<Comparative Example 1>
In the preparation of (1) a cathode side diffusion layer and an anode side diffusion layer of Example 1, the mean flow pore size 22 .mu.m, a bulk density 0.47 g / c ^{m 3,} thickness 188 [mu] m, basis weight 88 g / ^{m 2} and a porosity 0. The same operation as in Example 1 was performed except that 73% carbon paper was used.
With respect to the obtained cathode side diffusion layer, the measured value P1 of the pressure loss of the diffusion layer was measured using the pressure loss measuring device 50 described above, and as a result, it was 0.9 kPa. Further, the theoretical value P2 of the pressure loss was obtained according to the above formula (1), and P1 / P2 was calculated and found to be 19.4. The evaluation results are shown in Table 3.

<Comparative Example 2>
In the preparation of (1) a cathode side diffusion layer and an anode side diffusion layer of Example 1, the mean flow pore size 14 [mu] m, bulk density 0.35 g / c ^{m 3,} thickness 204Myuemu, basis weight 71 g / ^{m 2} and a porosity 0. The same operation as in Example 1 was performed except that 80% carbon paper was used.
With respect to the obtained cathode side diffusion layer, the measured value P1 of the pressure loss of the diffusion layer was measured using the pressure loss measuring device 50 described above, and as a result, it was 1.3 kPa. Moreover, the theoretical value P2 of pressure loss was calculated | required according to the above-mentioned Formula (1), and it was 25.7 as a result of calculating P1 / P2. The evaluation results are shown in Table 3.

<Comparative Example 3>
In the preparation of (1) a cathode side diffusion layer and an anode side diffusion layer of Example 1, the mean flow pore size 25 [mu] m, bulk density 0.27 g / c ^{m 3,} thickness 185 .mu.m, basis weight 50 g / ^{m 2} and a porosity 0. The same operation as in Example 1 was performed except that 84% carbon paper was used.
With respect to the obtained cathode-side diffusion layer, the measured value P1 of the pressure loss of the diffusion layer was measured using the pressure loss measuring device 50 described above, and as a result, it was 0.4 kPa. Further, the theoretical value P2 of the pressure loss was obtained according to the above-described formula (1), and P1 / P2 was calculated and found to be 1.6. The evaluation results are shown in Table 3.

<Comparative Example 4>
In the preparation of (1) a cathode side diffusion layer and an anode side diffusion layer of Example 1, the mean flow pore size 12 [mu] m, bulk density 0.33 g / c ^{m 3,} thickness 208Myuemu, basis weight 68 g / ^{m 2} and a porosity 0. The same operation as in Example 1 was performed except that 81% carbon paper was used.
With respect to the obtained cathode-side diffusion layer, the actual measurement value P1 of the pressure loss of the diffusion layer was measured using the pressure loss measuring device 50 described above, and as a result, it was 1.79 kPa. Moreover, the theoretical value P2 of pressure loss was calculated | required according to the above-mentioned Formula (1), and P1 / P2 was calculated, and it was 44.5. The evaluation results are shown in Table 3.

<Comparative Example 5>
Instead of the conductive porous sheet as the cathode-side microporous layer of Example 5, a conductive porous sheet having a pore diameter of 0.1 μm, a thickness of 48 μm, and a water pressure of 202.5 kPa was used. The same operation as in Example 5 was performed. The evaluation results are shown in Table 3.

<Comparative Example 6>
In the preparation of the cathode side microporous layer mixed paste of Example 1, 12 g of carbon “Vulcan XC72R” manufactured by Cabot Corporation, tetrafluoroethylene-hexafluoropropylene copolymer FEP dispersion “FEP” manufactured by Mitsui DuPont Fluorochemical Co., Ltd. The same operation as in Example 1 was carried out except that 20 g of “120-JRB” (solid content concentration 54%) and 155 g of ethylene glycol were weighed and mixed.
The pore diameter of the obtained cathode-side microporous layer was 12.1 μm as measured using a palm porometer manufactured by PMI. Moreover, thickness was 39 micrometers and the water permeation pressure measured according to the above-mentioned measuring method was 3.2 kPa. The evaluation results are shown in Table 3.

FIG. 4 is a diagram showing the relationship between P1 / P2 and the terminal voltage (1.25 A / cm ² ) based on the results of Tables 2 and 3. As shown in FIG. 4, Examples 1 to 3 in which P1 / P2 is in the range of 2 to 15 are 50 ° C. and Comparative Examples 1 to 4 in which P1 / P2 is out of the range of 2 to 15. It can be seen that high power generation performance is exhibited under any temperature condition of 70 ° C. From this result, it was confirmed that according to the present invention in which P1 / P2 is set in the range of 2 to 15, high power generation performance can be stably obtained in a wide temperature range.

FIG. 5 is a diagram showing the relationship between the water permeation pressure of the microporous layer and the terminal voltage (1.25 A / cm ² ) based on the results of Tables 2 and 3. As shown in FIG. 5, Examples 1 and 4 to 6 in which the water permeation pressure of the microporous layer is within the range of 5 to 180 kPa are compared with Comparative Example 5 and the water permeation pressure of the microporous layer is outside the range of 5 to 180 kPa. Compared to 6, it was found that the cathode gas inlet relative humidity was higher under both humidification conditions of 25% and 73%. From this result, it was confirmed that according to the present invention in which the hydraulic pressure of the microporous layer is set within the range of 5 to 180 kPa, high power generation performance can be stably obtained regardless of the humidified state.

  From the above, according to the present invention in which P1 / P2 is set in the range of 2 to 15 and the water permeation pressure of the microporous layer is set in the range of 5 to 180 kPa, it is not affected by the humidified state in a wide temperature range. It was confirmed that stable and high power generation performance can be obtained.

1. Solid polymer fuel cell (fuel cell)
DESCRIPTION OF SYMBOLS 10 ... Diffusion layer structure 11 ... Diffusion layer 12 ... Microporous layer 20 ... Membrane electrode structure 21 ... Solid polymer electrolyte membrane (electrolyte membrane)
22 ... Cathode electrode catalyst layer 30 ... Separator 31 ... Oxidant gas flow path

Claims (2)

A diffusion layer structure of a fuel cell disposed in a membrane electrode structure in which electrodes are provided on both sides of an electrolyte membrane,
A diffusion layer, and a microporous layer mainly formed of carbon and fluororesin and formed on the diffusion layer on the electrolyte membrane side,
The actual value of the pressure loss defined by the following equation (1) is defined as P1, where P1 is an actual measurement value of the pressure loss that occurs when air of ² L / min flows through the diffusion layer having a permeation area of 1.86 cm ^2. When P2, the ratio P1 / P2 of P1 to P2 is adjusted within the range of 2 to 15 as a parameter correlated with the flexibility of the pores in the diffusion layer ,
A diffusion layer structure for a fuel cell produced by adjusting the water permeation pressure of the microporous layer within the range of 5 to 180 kPa as a parameter correlated with the moisture retention of the membrane electrode structure.

[In the formula (1), the thickness represents the thickness (μm) of the diffusion layer, the porosity represents the porosity (%) of the diffusion layer, and the average flow pore diameter is the average flow pore diameter of the diffusion layer. (Μm). ] A method for producing a diffusion layer structure of a fuel cell disposed in a membrane electrode structure in which electrodes are provided on both sides of an electrolyte membrane,
A diffusion layer, and a microporous layer mainly formed of carbon and fluororesin and formed on the diffusion layer on the electrolyte membrane side,
The actual value of the pressure loss defined by the following equation (1) is defined as P1, where P1 is an actual measurement value of the pressure loss that occurs when air of ² L / min flows through the diffusion layer having a permeation area of 1.86 cm ^2. When P2, the ratio P1 / P2 of P1 to P2 is adjusted within the range of 2 to 15 as a parameter correlated with the flexibility of the pores in the diffusion layer,
A method for producing a diffusion layer structure for a fuel cell, comprising adjusting the water permeation pressure of the microporous layer within a range of 5 to 180 kPa as a parameter correlated with moisture retention of the membrane electrode structure.

[In the formula (1), the thickness represents the thickness (μm) of the diffusion layer, the porosity represents the porosity (%) of the diffusion layer, and the average flow pore diameter is the average flow pore diameter of the diffusion layer. (Μm). ]

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